280 PIIOCEEDIXGS OF THE NATIONAL MUSEUM. vol.xxiv. 
Second, The convexity or angulation of the whorls is another marked 
feature. This, it will be seen, is exhibited in various degrees, by com- 
paring ligs. 1-4 with 7, 9, 12, and others, until the extreme of angula- 
tion and tabulation is reached, as in examples 8 and 11, where, as in 
the latter, the flattening of the upper part of the whorls is remarkably 
uniform and produces a turreted effect. Both 8 and 11 are exceedingl}^ 
rare varieties, only one of each in the many thousands of specimens 
critically examined. 
Third. The aperture or mouth, it will be noticed, is quite variable, 
both in shape and size, often small, as in tig. 14; the edges simple or 
thin, generally continuous; again more or less thickened or flattened 
and flaring, as in ligs. 6, 12, and 14; sometimes closely appressed to 
the basal whorl, frequently barely touching, and often free or not 
touching it. These latter aspects suggest an umbilicus, as in fig. 13, 
but the gap is only superficial. In fig. 10 it will be seen the lip is not 
continuous. The aperture may be round, or very nearly so, rounded 
ovate, ovate or angulated ovate, as in fig. 11. The length of the 
aperture and its position as related to the axis of the shell varies in 
different examples. Compare 9, 11, and 12 with 1, 3, 5, and 10. In 
11 there is a sinuous curving callous or fold in the umbilical region 
just above the mouth. 
Gould remarks in his description of protea: " It varies greatly 
* * * in the relative proportions of length and breadth." He also 
noticed the strength of the sutural definition; and Conrad mentions 
the general scalariform aspect which is so strikingly exhibited in 
many of the examples, whether plain or sculptured. 
VARIATION IN SCULPTUPE. 
First. Plain smooth shells like figs. 1 and 2 (with convex whorls), 
from Death Valley, at Saratoga Springs (Nelson and Bailev); in the 
Mexican States of Michoacan (Duges), and Durango (Frauenfeld); near 
Roswell, New Mexico (Tinsley-Pilsbry). The eroded Sevier Lake, Utah, 
specimens (Yarrow) may be included with the above. Then follow the 
smooth-surfaced forms, with whorls somewhat angulated on the upper 
part, as shown in fig. 6, and the unique, strongly angulated example, 
fig. 8. In this the pronounced angulation of the whorls points toward 
my species, Pyrgulopsls nevadensls of Pyramid Lake. 
Second. Spirally Urate or threaded (whorls convex), the lirse more or 
less prominent, as in figs. 3 and 4. All of Orcutt's Dos Palmas Springs, 
ten living specimens are of this pattern. In fig. 9 is shown an unusally 
robust example (whorls slightl}^ angulated above), the lirte distinct, but 
much less conspicuous than in the slenderer, more strongly angulated 
and threaded fig. 10. In fig. 11 the angulation of the part of the 
whorls is extremely developed, passing into tabulation or flattening, 
producing a turreted effect, and the spiral threading numerous, closely 
set, and well defined. 
